The present invention relates to a seal for a shaft running through the wall of the housing of a working chamber filled with plasticized resin under pressure as part of a resin processing machine.
More specifically the invention is concerned with mechanical seals for squeeze roll presses for recycling scrap synthetic resin by producing a regenerate therefrom. Such a squeeze roll press is described in the German Pat. No. 2,700,846. The invention will be explained with reference to such a squeeze roll press, although at the same time being generally well suited for use in connection with other resin processing machines operating at high pressures and temperatures.
A number of different requirements have to be met by a shaft seal of this sort. It has to be able to hold back the resin under a high pressure in the working chamber, because this pressure is necessary not only for the plasticization but also for the expulsion of the plasticized resin from the working chamber without any other means, as for example a conveying worm or screw. Because during operation of the machine one-sided loading may cause the shaft to wobble or run eccentrically, the seal has to be such that it makes allowance in this respect and still gives a full sealing function. When the machine is started up and there is a sharp rise in temperature, the seal has to be in a position of allowing for expansion, more specially of the shaft, without becoming functionally unreliable. Lastly, the seal should be able to be dismounted without it being necessary for the resin processing machine to have to be dismantled as well so that in fact the replacement of defective parts is relatively simple.